1. Field of Invention
This invention relates to a mark structure for measuring the alignment accuracy between a former layer and a latter layer with electron beam inspection (EBI), and to a method for measuring the alignment accuracy between a former layer and a latter layer using the mark structure and an electron beam.
2. Description of Related Art
Conventionally, the alignment accuracy (AA) between photo layers is measured using box-in-box (BIB) AA verniers, or testkeys that require an electrical test for the measurement. However, an AA vernier takes a large area of about 40×40=1600 μm2, and a testkey also takes such a large area due to the requirement of large test pads for the probing in the wafer acceptance test (WAT). Hence, the AA vernier or testkey can be formed in the scribe line regions only but cannot be embedded in the product, so that the AA window derived therefrom is not so accurate.
Moreover, the pattern of the AA vernier cannot be the same as that of the product so that the alignment accuracy derived therefrom is even less correct than that derived from the testkey. In addition, the alignment margin cannot be derived using an AA vernier. On the other hand, as a part of the WAT, the electrical test done to the testkeys for the measurement of the alignment accuracy takes much time so that the throughput is adversely affected.